The present invention relates to web processing, and more particularly relates to a method and apparatus for processing webs by exposing them to radiant energy.
In numerous industrial applications, webs of flat materials such as paper, plastics, foils and the like are treated by exposing them to radiant energy. Ordinarily, the materials to be treated are supplied as a series of semi-continuous webs. The supply coil containing each web is loaded into a payout stand and the leading end of the web is threaded along a transport path to a takeup stand. The web is then transported along the path by winding it onto a takeup coil at the takeup stand while unwinding it from the supply coil at the payout stand. As each web is fed along the transport path in this manner, beams of radiant energy impinge upon it and treat it. One application of this technique is the perforation of cigarette tipping paper by exposure to pulsed beams of light from a laser.
Although webs can be treated at extremely high speeds by certain types of radiant energy devices, the productive capacity of the apparatus heretofore available for such treatment has been significantly impaired by loss of productive time during unloading and reloading. With the apparatus of the prior art, the radiant energy emitting portion of the apparatus has been idle while each treated web is unloaded from the takeup stand and the next web is loaded into the payout stand and threaded along the transport path. Modern apparatus for perforating cigarette tipping paper with laser light can process a web of paper at linear speeds of up to 7,000 feet per minute. Even if each web is as long as can be accommodated in a coil of reasonable size, apparatus running at this speed will require reloading after only about 2 to 3 minutes of operation. If the apparatus is idle for only 1 minute during each unloading and reloading cycle, from 25 to 33 percent of its productive capacity will be lost.